I need help with plans

[Pilgor]

My friend just built a dual chambered pneumatic spud cannon. It looked good so i was about to use his plans. but then his gun blow up. He was using pressure rated sch 40 pvc. does anyone here having any safe dual chambered pneumatic potato guns.
and do not ask to see the plans i have because i have deleted them and so has my friend.

thanks alot in advanced.

[bigbob12345]

Your friend was probably using sch40 pressure rated pipe but his fittings were dwv thats why it exploded. Did he use bell reducers?Because they are almost all the time dwv.Just use your friends design but use pressure rated fittings. It is sometimes hard to find pressure rated fittings above 2in so if you cant find them buy them from mcmaster http://www.mcmaster.com/

[MrCrowley]

Just a warning, Sch 40 doesn't mean it's pressure rated. It's a thickness rating, not a pressure rating.

What you need to look for is 'NSF-PW' on the pipe or fittings, which is always pressure rated.

[schmanman]

Just a warning, Sch 40 doesn't mean it's pressure rated. It's a thickness rating, not a pressure rating.

What you need to look for is 'NSF-PW' on the pipe or fittings, which is always pressure rated.

I love it how crowley knows more about our plumbing system than most americans do.

I find it humorous.

[hi]

either that or you over pressurized it. just because 2'' pipe is rated for 280 psi doesnt mean you can take it to 280 psi. in fact its not safe to do much more that 150 psi in my opinion. it could also be that he had faulty weld joints, or maybe the pipe was defective... it could be anything. if you do it right then that sort of thing wont happen.

[BrianMigs]

what does a bell reducer look like? and how can some people on here tell if certain parts are dwv, especially if its all ready painted over?

[MrCrowley]

Just a warning, Sch 40 doesn't mean it's pressure rated. It's a thickness rating, not a pressure rating.

What you need to look for is 'NSF-PW' on the pipe or fittings, which is always pressure rated.

I love it how crowley knows more about our plumbing system than most americans do.

I find it humorous.

I get it from you guys, so you better be right

'Spose it's like a language, and you just pick it up as you go.

And it's very handy if you speak the native language of the country you reside in, if you know what I mean.


Some guy at a hardware store yesterday was trying to sell me this crappy car compressor, he said he used it on forklift tyres, which are (according to him) very high pressure.

I ask how high it pumps, (while catching a glimpse of '250PSI' written on the box) and he said, 'oh about 300BAR'.

I just started laughing and asked if he knew his BAR and PSI, he said he did and kept saying forklift tyres are very high pressure. Then I told him 300BAR is about 4500psi, which you need hydraulic fittings for and i'd like to see a plastic pump get 1/10th that.

It still had no effect on him, he must not realise how high of a pressure 4500psi is, and the box of the pump had '250PSI' written about 10x all over it.

[schmanman]

from the structure of the part. the sockets are not as deep, the reducers are entirely different, and the walls of said part are much thinner.

[pizlo]

To be safe you could spend a bit more and go metal. I don't think anyone here has ever seed a metal spud gun explode.

[hi]

you can tell because DWV parts have their own shape that pressure rated parts do not come in, and vis versa.

also, dont put a lot of stress or strain on the fittings because fittings are usually the weakest link in a cannon, even if they are pressure rated, so putting stress on them makes it that much more likely to fail.

[MrCrowley]

what does a bell reducer look like? and how can some people on here tell if certain parts are dwv, especially if its all ready painted over?

This is a bell reducer:


If a part is DWV, it should only say DWV and maybe Sch 40 on the fitting/pipe.

On fittings the writing is usually raised and can be read once painted over, with pipe, if you have enough layers of paint you probably can't read it.

Don't Worry about identifying DWV pipe and fittings, more pressure rated fittings.

To find out if a fitting is pressure rated, it should have 'NSF-PW' and it may also have Sch 40 (or 80,120 etc) on it. IIRC American fittings don't have a pressure rating on them, but if they have NSF-PW, you're okay, it will be rated.

For pipe, it should have 'NSF-PW Sch 40 (or 80,120, etc) XXXPSI @73F'

XXXPSI, is the pressure rating, it changes depending on the Schedule rating and the diameter of the pipe. The pipe may have a different temperature rating, but the most common say '@73F'.

The pipe may also have 'DWV" written on it, as long as the pipe has a pressure rating, e.g '300PSI @73F' you're okay.

If it doesn't have 'NSF-PW' or pressure rating, chances are it's DWV.

Edit:

This is a PRESSURE RATED PVC 90* bend:


This is a DWV PVC 90* bend, non-pressure rated:


As you can see, the difference is very obvious.

You can get fittings that look DWV, but I doubt you will find them at Home Depot or Lowes, usually they're only found online.

[pizlo]

what does a bell reducer look like? and how can some people on here tell if certain parts are dwv, especially if its all ready painted over?

This is a bell reducer:


If a part is DWV, it should only say DWV and maybe Sch 40 on the fitting/pipe.

On fittings the writing is usually raised and can be read once painted over, with pipe, if you have enough layers of paint you probably can't read it.

Don't Worry about identifying DWV pipe and fittings, more pressure rated fittings.

To find out if a fitting is pressure rated, it should have 'NSF-PW' and it may also have Sch 40 (or 80,120 etc) on it. IIRC American fittings don't have a pressure rating on them, but if they have NSF-PW, you're okay, it will be rated.

For pipe, it should have 'NSF-PW Sch 40 (or 80,120, etc) XXXPSI @73F'

XXXPSI, is the pressure rating, it changes depending on the Schedule rating and the diameter of the pipe. The pipe may have a different temperature rating, but the most common say '@73F'.

The pipe may also have 'DWV" written on it, as long as the pipe has a pressure rating, e.g '300PSI @73F' you're okay.

If it doesn't have 'NSF-PW' or pressure rating, chances are it's DWV.

This man speaks the truth. we should compile all of this and everything else he has ever said into a "bible"and make newbs read it.

[BrianMigs]

Hey whaddya know, I have a 3" to 1" bell reducer on my cannon, crap. LOL

I have taken it up to 70PSI multiplt times, do I have a ticking time bomb?

I am going to go check all my fittings on my gun, they are all sch40 though, that I am sure of. Cheers

[MrCrowley]

I am going to go check all my fittings on my gun, they are all sch40 though, that I am sure of. Cheers

Still doesn't matter, what you need is the 'NSF-PW' on the fittings and 'NSF-PW' and/or a pressure rating in PSI on the pipe.

Probably not a ticking time bomb, but I wouldn't trust it personally, you never know when it could blow.

[bigbob12345]

You dont really have a ticking time bomb but try not to use it above 60psi even then it is dangerous I would recomend sawing off the bell reducer and replacing it with a bushing.